1. Field of the Invention
The present invention relates to a method for adhering a rubber composition to a metal material.
2. Description of the Prior Art
Various methods for adhering a rubber composition to a metal material have been heretofore known. For example, the following methods have been proposed.
1. A method comprises subjecting metal surfaces to a specific treatment, applying polyisocyanate layer thereon and then putting a rubber layer on the polyisocyanate layer and heating the resulting assembly (Japanese Patent No. 225,414).
2. A method comprises coating a primer composed of chlorinated elastomer-butadiene-methyl methacrylate copolymer on metal surfaces (Japanese Patent No. 468,417).
3. A method comprises coating a rubber composition containing sulfur and peroxide on metal surfaces (Japanese Patent Application Publication No. 5,145/70).
In these methods, the operating steps should be increased and in some case, a particular processing installation is necessary and further there are problems in the storage stability of primer, and in the inflammability and poison of solvent.
A large number of methods wherein certain compounding agents are mixed with rubber compositions and the resulting rubber compositions are adhered to metals by vulcanization have been proposed. For example, a method comprising compounding a metal naphthenate, mainly cobalt naphthenate to a rubber; a method comprising compounding resorcin hexamethylenetetramine and silica to a rubber; and a method comprising compounding a metal oxide and one of a chlorinated paraffin and a chlorinated polymer to a rubber are known. However, in these methods, when NBR or a blend consisting mainly of NBR is used as the rubber, the adhesion of the rubber composition to zinc is very low and such methods are not practical.
For the adhesion of NBR to zinc, it has been heretofore known that ferric chloride can be compounded in NBR. However, in this method the adhesion of NBR to zinc is improved to a certain degree but rust is formed in the working machine and NBR sticks considerably to the roll and thus this method is not preferable in practice.
In addition, brass plating on a metal is a useful process for improving the adhesion and this method has been heretofore carried out, but in this case, when water or moisture of more than a certain amount is present upon the materials, the adhesion is quite poor and particular attention must be paid to process adjustment and to the storage of the material.